This invention relates generally to electric steam boilers, and more particularly to an electrode boiler having a heating zone defined by a pair of spaced support walls within which is located a plurality of insulating members which create a high resistance to electrical current flow in a direction perpendicular to the support walls.
In immersion-type electrode boilers, electrodes connected to an appropriate source of electrical power are either completely or partially immersed within an electrolyte to be heated. The electrical current density at the electrode surfaces must be kept below that at which unacceptable electrochemical corrosion of the electrodes would occur. As electrical conductivity of the electrolyte increases (e.g., by use of high conductivity ("dirty") water), resistance to flow of electrical current decreases so that the current density within the electrolyte, and consequently at the electrode surfaces, increases. The maximum current density tolerable by the material of the boiler electrodes requires use of purified water, or at least water having a conductivity no greater than a certain predetermined level, when using prior art immersion-type electrode boilers.
A number of techniques have been applied in the prior art, as described in U.S. patent application Ser. No. 032,116 filed Apr. 23, 1979, of T. A. Keim, assigned to the instant assignee, and incorporated herein by reference, to attempt to limit current density within the boiler cell to a level tolerable by the boiler electrodes. The above-mentioned U.S. patent application Ser. No. 032,116 describes a system of insulators designed to limit the current path volume within the electrolyte, so that the maximum current density within the electrolyte would not exceed that tolerable by the boiler electrodes.
An object of the instant invention is to provide tortuous high resistance paths to electrical current flow in the direction between the boiler electrodes, and simultaneously to provide paths for steam bubble removal in the direction generally perpendicular to the direction of current flow through the electrolyte.
A further object of the instant invention is to provide an electrode boiler configuration in which steam generation is confined to a volume separated from the electrodes of the boiler.
A further object of the instant invention is to provide a boiler system whose electrical resistance can be readily changed to accommodate a variety of electrolyte conductivities.